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Topic: Treadmill Dyno (Read 128283 times)

Adjusting the AFR is difficult, because during a burn, it varies widely, from super rich to super lean. This causes the engine not to want to start. Also, it's impossible to tune the AFR without the correct load. The carb has an AFR screw for the low end and the main needle for the high end. The carb needed the needle moved a bit, but once you do that, the AFR and idle screws need tuned a lot, making this a risky decision in the middle of a race day. You can only drive the car on the track, so you wouldn't get many chances to tune the engine if you messed it up. Also, the low end AFR screw is super sensitive, so it's hard to play with. Varying air temperature for the intake also makes things a challenge, as the car heats up once the lid is put on.... this year, the nose of the car got so hot under where the front window was, that it was getting soft. Some teams put aluminum foil under the driver's feet... I can't imagine that helps visibility out of the already sketchy windows.

It's interesting, because every year, the weather conditions are different, from windy to calm and then from cold to hot and sunny to stormy. Yet most teams aren't prepared for varying situations. Being able to have your car run at it's best in any weather condition is important. In the 5 years I've been there, I bet the insides of the cars has varied from the coldest to the hottest by 100F+. Just goes to show, learning how to make the best supermileage car takes more than a year or two... it really takes several generations of students to pass on the knowledge of all of the lessons learned.

And another thing that is so great is that there is no perfect answer for a car and that there is always room for improvement. A perfect car in the perfect conditions could achieve 6-10,000 mpg... yet only two teams in SAE history have cracked the 3,000 mpg barrier and only a handful to break 2k mpg.

No, No, No, and No. We had an external O2 sensor that we could clamp to the end of the exhaust pipe, but that's it. Throttle position was up to the driver. On our EFI test engines, we have MAF's, but not on the carbureted engines. I have seen teams who have attempted a servo controlled throttle to vary the throttle % during a burn... fairly complex to effectively do so.

The engine in the car this year was the 53 cc SOHC ~14-15:1 CR custom head with dual spark plugs. It ran very well and experienced no problems that we know of, just that the AFR was way too rich.

The rotary valve for the SAE car has not been tried again. It needs to be re-sealed and glued to be run again. The only reason to do this is for the satisfaction to see it run, since no one would risk running it at competition. My homemade rotary valve still needs some attention and probably a bit of tuning on the AFR front..... which is hard to do with no O2 sensor and a coil wrap pull start.

Here is a video of my personal rotary valve 3.0 design running. Probably my best engine video yet. Completed the whole thing over Christmas break. This version of the engine already has more run time on it than all of the previous versions combined. I can't wait to make a dyno for it.

Version 3 has a floating bronze seal in the center that gets pushed up by the combustion pressure. The springs are there to lightly pull up so it doesn't fall down during the intake stroke and cause a vacuum leak. The engine was designed to be a 10.2:1 compression ratio, but currently is about 8:1 since the seal is up in the air a bit. A compression test revealed a healthy 135 psi.

In other news, we also found the reason(s) why our mini 53 cc engine wasn't very efficient at competition. Basically, it was severely worn out, with the valves, valve guides, and valve seats pretty much past their usable lifespans. A new set of valves, seats and some sleeves for the guides will get it back to new again. This explains the halfway decent efficiency at high rpm's and very low efficiency at lower rpms.

The brass piece is a cylinder that goes all the way to the combustion chamber. It has the sparkplug, half-pipe journal surface, the port and the combustion chamber milled into it. On the outside, there is an o-ring and some teflon backers for sealing.

The brass piece floats and is pushed up by the combustion pressure. The springs prevent it from dropping back down.

The pipe is more complicated than I thought. How hard is it to make?Is it machined as one piece? Can the machining of each path be completed from the port side, or do you have to do some tricky things at the bottom of the hole bored into the bar? Now that I see the way the passages are separated, I wonder if maybe an insert that pushes in from one end would be easier to make.

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No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.

Last Friday, we clamped the engine to a table and let it run for 73 minutes straight! The previous record was 6 & 1/2 minutes. It was idling at 1100 rpm with a few minutes of goosing the throttle (up to 4k) and low as ~800 rpm. For the last 10 minutes, we upped it to ~2k rpm... it finally got a bit hot on the exhaust end and I think burned the oil off the edge of the seal, which then greatly increased the friction and lead the end of the valve to turn blue (measured at 400F). You could hear the #25 chain start to groan under load, so I shut it off. The head/ block were about 260F, which isn't too bad considering the complete lack of cooling. There were some bubbles in increasing intensity coming around the seal near the end, which leads me to question how well the o-ring held up. I can't wait to tear it apart. Next step is to put it on my friend's go-kart.

The pipe is more complicated than I thought. How hard is it to make?Is it machined as one piece? Can the machining of each path be completed from the port side, or do you have to do some tricky things at the bottom of the hole bored into the bar? Now that I see the way the passages are separated, I wonder if maybe an insert that pushes in from one end would be easier to make.

We've made two valves at this point. Both started with precision ground steel, which takes care of the OD. It is machined as once piece, drilled from both ends and then each of the openings in the center get milled on a mill or 4-axis lathe. Generally, you can't mill the transition between the drill operation and the mill operation to be very smooth, so some dremmel work is required. You can make the path better for air flow, but it increases the machining complexity. A nice multi-axis lathe could do a better job... kind of like how custom intake runners are machined in normal engine heads for race cars.

You have too many files open Taylor.If I did that on my computer, Inventor would crash!

That's nothing. Running CFD, I pushed my laptop to 59 Gb of RAM used (16 Gb actual ram). A solid state disk drive helps in that endeavor. At work, at times I have had 40+ applications open at once (I do a lot of data mining across different programs) and it only has 4 Gb of ram and the motherboard tends to only allow me to use 2.2 Gb of it... the rest of it gets swapped to an encrypted disk drive, which is really slow.

I tore the head apart last night and everything looked just fine. O-rings were good and the sealing surface wasn't too worn or had any major scratches. There was some gooey tar in the combustion chamber and smeared around the valve, so we are going to advance the "cam" timing by a few degrees and see if that helps. On the plus side, any carbon or tar build up helps seal it better. While we had it apart, we machined the spark plug countersink so it's now flat, which should stop some of the leaking. The exhaust was nice and clean, but the intake had some of the tar, so we believe some of the charge is going back into the intake while running.

Have you given any thought to the air exchange process and how complete the burning may be? Air/fuel mix swirling about the chamber - you seem to be equipped to do CFD analysis, so have you done any for this subject? Have you done any exhaust gas analysis? (Maybe you've mentioned it before... this thread is getting really long!)

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No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.

I haven't hooked an AFR gauge to any of my rotary valve engines yet. I have done some CFD on version 1.0. This afternoon, I just set up version 3.0 in CFD, so I shall see what it looks like, especially with a computer that is 3X faster and 4X more RAM to play with.

Mixing of the fuel and the air should be very good compared to a poppet valve configuration.

Version 1.0 theoretically had a volumetric efficiency of 107% at 3,000 rpm based on my basic simulation. Here is a screen shot from it and a video of some particles from the end view.https://www.youtube.com/watch?v=uG0dRqNiBQk

My current engine uses a #25 chain and a 2:1 ratio for the drive to the rotary valve. Version 1 used a Kevlar stranded timing belt and we broke several nylon stranded belts due to the high loads from the aggressive cams that held the valve down.

Finally hooked the rotary valve engine up to the dyno and was able to do two runs. Both were at full throttle. The first one was just to measure peak horsepower, which yielded 2.4 shaft horsepower at ~3800 rpm. Not bad considering the stock engine is only rated for 1.5 hp. The second run, we did a fuel economy test and it yielded 13.4% efficient at 2.3 hp. That kind of efficiency is comparable to a stock 3.5 hp briggs. Both the peak power and efficiency numbers could of been higher due to a pretty large groove that was forming in seal and was causing it to leak. After those runs, it was misfiring and not holding idle very well... so it looks like it is time build a new seal and possibly a new valve. The current "valve overlap" between the intake and the exhaust is 5 degrees. I plan on making that a bit more aggressive. The question is how much. I also need to question the heat transfer ability between the seal and the head, as it was pushing ~330F after the dyno runs.

We designed and machined a new seal, now with 36 degrees(crankshaft) of valve overlap between the intake and exhaust vs the previous 11. Now it sounds more like a performance oriented engine and shoots a few more flames. It definitely seems to have more power, and we can't wait to put it back on the dyno. We also swept the shape of the port for better flow on the intake stroke.

Last night, we replaced the hoses and fittings on the fuel system so it stopped leaking, so we tried to use all the gas in the tank. Managed to get the center of the valve up to ~550 F, at which point it decided it didn't want to idle much more. I think the gooey oil that cakes itself to the valve and seal started to melt and caused more leaks. The intake gases do a good job of cooling the one side of the valve and the part between the chain and the seal was about 350F.

Bringing back this thread to show off the next stage of the rotary valve engine development!

Now in a 1999 BMW 328is 2.8L inline 6 engine. A first in many respects, including converting a modern production car, an Inline 6, and a BMW. It has some fun features including muffler bearings, exhaust bearing coolant, coolant running through a floating seal around the sparkplug, contra-rotating valves, 6 velocity stacks with no obstructions going right into the cylinder, custom double bevel gear box with homemade "cam lobe", multi-tiered oiling system, and a fully re-mapped cooling system that has many clear hoses.

Over 700 components, fully integrated into the stock engine bay.......... so bolts right up to the exhaust, all the sensors and hoses and stock intake. No programming of the ECU has taken place yet (many people said this would never work). We machined about half the components ourselves to save cost, but the bigger ones exceeded the capacity of our tools so they had to be sent out.

I'm getting really close to taking it back to the dyno to see how she fairs. Still working out some kinks, but it has over an hour of run time on it and about 3 miles of hard driving in my back yard and up and down my driveway. There have been moments where it seems like it has more power than the stock engine. Sealing seems to be much better than the ego-kart engines and it has good compression and spark.

And I have to give some congratulations for BMW making such a robust starter motor.....